1. Technical Field of the Invention
The present invention relates to an aluminum brazing sheet used in a header, a side plate, etc. of an automotive radiator, and more particularly, to an aluminum brazing sheet for brazing which has high strength, high formability and excellent brazing property.
2. Description of the Related Art
Conventionally, as an aluminum brazing sheet for brazing used in a header, a side plate, etc. of an automotive radiator, Alxe2x80x94Mn based aluminum alloy of JIS3003 alloy, etc. as a core material, Alxe2x80x94Si based aluminum alloy of JIS4045 and JIS4343 alloys, etc. as a brazing filler material and Alxe2x80x94Zn based aluminum alloy as a cladding material serving as a sacrificial anode have been used. However, the brazing sheet comprising the core material composed of Alxe2x80x94Mn alloy of JIS3003 alloy, etc. has strength of about 110 MPa after the brazing so that the strength thereof is not sufficient and corrosion resistance thereof is not sufficient. Although it is effective that Mg is added to a core material in :order to improve the strength after the brazing, in a Nocolok Flux Brazing method, the brazing property of a brazing sheet in which Mg is added to a core material is significantly degraded so that it is not preferable to add Mg to the core material.
Thus, as techniques to improve strength after the brazing without degrading the brazing property, various proposals have been made as described in Japanese Patent Laid-Open Nos. Hei 4-193926, Hei 5-230577, Hei 6-145859 and Hei 6-212331, etc. Publications.
However, the prior arts described in the publications had a problem that a further thinning of the brazing sheet cannot be accomplished.
Since Si was added to a sacrificial anode cladding material for high strength in the prior art disclosed in Japanese Patent Laid-Open No. Hei 4-193926 Publication and Fe was not restricted in Japanese Patent Laid-Open No. Hei 5-230577 Publication, formability is low, and cracking tends to occur during pressing process of a header.
Since much amount of Zn were added to a sacrificial anode cladding material in Japanese Patent Laid-Open Nos. Hei 6-145859 and Hei 6-212331 Publications, formability is low, and cracking may occur during pressing process of a header.
Further, since Mn was added to a sacrificial anode cladding material for the high strength in the prior art disclosed in Japanese Patent Laid-Open No. Hei 6-212331 Publication, formability is low, and cracking tends to occur during pressing process of a header.
As described above, it was difficult to obtain a brazing sheet having all of features of strength after the brazing, brazing property and: formability in the prior arts.
However, in a heat exchanger such as an automotive radiator and a heater core, there have been demands for thinning of material to accomplish lightweight and manufacturing cost-down so that there have been also strong demands for the thinning of aluminum brazing sheet used in the brazing.
Further, the conventional high strength materials had a problem that warping or spring back is generated in case of forming or punching a plate material so that stable shape cannot be maintained.
An object of the present invention is to provide an aluminum brazing sheet having high strength after the brazing, excellent brazing property and improved formability.
An aluminum brazing sheet according to the present invention comprises a core material formed of an aluminum alloy having a composition restricting Mg to less than 0.3 wt % and Fe to not more than 0.2 wt %, and containing more than 0.2 wt % and not more than 1.0 wt % of Cu, 0.3 to 1.3 wt % of Si, 0.3 to 1.5 wt % of Mn land the balance of Al and inevitable impurities; a brazing filler material formed on one surface of the core material by Alxe2x80x94Si based aluminum alloy; and a cladding material formed on the other surface of said core material. Said cladding material is formed of an aluminum alloy containing less than 0.2 wt % of Si, 2.0 to 3.5 wt % of Mg, not less than 0.5 wt % and less than 2.0 wt % of Zn and the balance of Al and inevitable impurities. The ratio of (cladding material hardness)/(the core material hardness) that is a ratio of the hardness of said cladding material to the hardness of said core material is not more than 1.5.
Said core material may contain not more than 0.3 wt % of Cr, not more than 0.3 wt % of Zr or not more than 0.3 wt % of Ti. The Mg content of said core material is preferably not more than 0.1 wt %.